A frequent way today to restore a damaged or lost tooth is to install a dental implant comprising a fixture in the adjacent jawbone tissue (maxilla or mandible) and replace the damaged or lost tooth with a dental prosthesis. A superstructure, such as an abutment, may be used as a connection between the dental prosthesis and the installed fixture.
An abutment may have an externally threaded portion formed in one piece with a prosthesis-supporting portion. The abutment is by means of its threaded portion screwed into the fixture which has an internal bore with a corresponding threaded portion. Thus, in this case, the abutment is a male dental component and the fixture is a female dental component.
An alternative to the one-piece abutment, is an abutment having a separate abutment screw. The abutment screw has an externally threaded portion and a screw head. When fastening the abutment to the fixture, the abutment is first mated to the fixture and then the abutment screw is inserted into a through-hole of the abutment so that the threaded portion of the abutment screw engages the internal threading of the fixture and the screw head is seated on a seat in the through-hole of the abutment. In this case the abutment screw may be regarded as a male dental component which is inserted into a female dental component in the form of an abutment.
Other examples of male/female dental components are bridge screws/bridge supports, guide pins, impression components and cylinders.
Manufacturers of dental components generally recommend a certain torque (normally in the region of 15-35 Ncm) to be used when the male dental component is finally tightened to the female dental component. For instance, a manufacturer may for a certain abutment screw recommend a torque of 25 Ncm when finally tightened to the abutment, typically when the screw head has touched the seat of the abutment.
If the applied torque is too low, the male dental component is not tightened adequately to the female dental component, which may lead to loosening of the male dental component. If loosened, the male dental component may in turn cause fractures in the female dental component.
On the other hand, if the applied torque is too high, the axially directed tensile stress becomes so high that the male dental component will break, the weakest point usually being below the first coronal revolution of the thread. The female dental component may also become damaged.
Unfortunately, dentists do not always use the recommended torque, but sometimes use a higher or a lower torque. Furthermore, a manufacturer may recommend different torques for different dental components or for different sizes of the same type of dental component. Thus, there is a risk of the dentist inadvertently applying a non-recommended torque.
An object of the invention is therefore to reduce the risk of dentists applying too low torques which may cause loosening of the male dental component and potentially ensuing fracturing of the female dental component, and also to reduce the risk of dentists applying too high torques with may cause the male dental component to break and potentially also damage the female dental component. This and other objects which will become apparent in the following, are accomplished by the invention as defined in the accompanying claims.